Dosimetry is an extension to the present fixed-site air pollution sampling systems. Previous to about 1950, air pollution measurements were concerned more with property effects than with health effects. There has been an increased requirement to correlate health effects with the quality of the air to which the general population is exposed. Prior to 1950, various investigators in the area of industrial hygiene was engaged in activity directed to workroom atmospheres. A considerable amount of the methods and instruments developed for industrial hygiene investigations have been adapted to the study of air pollution measurements.
In the area of industrial hygiene, it has been recognized that, at an early date, it is desirable to provide workers with portable instrumentation to measure exposure or dosage to dust, certain gases and radiation. There has been some development in miniature sampling instrumentation for installation on some segments of the worker population. For example, a passive personal monitoring device for gaseous contaminates based on molecular diffusion of the gas to be measured, such as sulfur dioxide, has been proposed (see "American Industrial Hygiene Association Journal," Vol. 34, pgs. 78-81, 1973).
Instrumenting workers with personal sampling equipment has met with certain implementation problems. Problems relating to subject performance include: failure to wear the equipment; failure to maintain the equipment; and failure to operate the equipment.
In the development of instrumental dosimeters, certain additional limitations have been encountered, including, but not limited to: size and weight (restriction on subject freedom of movement); cost (inhibits testing by large population segment); need for power supply; high maintenance requirements; drift in instrument response (leads to erroneous measurements); and sensivity to changes in temperature and humidity.
Another approach has been to use indicator tubes, for field measurement. However, these show poor accuracy (&lt;.+-.50%) due to: variability in quality control in tube manufacture; error in test subject judgement; degradation of color developed with time; variation in sample flow rate with time (a flow-through system is required); and variation in ambient temperature (affects reaction rate).
A third method has been to use exposure plates, such as badges, which are completely passive. This approach has been highly successful for radiation badges.
These nonburdensome radiation badges, which are in widespread industrial use, are virtually fool-proof if simply worn. The sensing elements are issued and collected periodically with the collected film being processed efficiently in a central location. An analogous system for air pollution dosimetry would be most valuable; however, the major limitation encountered is that a badge of this nature does not respond to pollutant concentration, but rather to a complicated interaction of concentration and ambient air circulation patterns. Thus, a personal passive dosimeter and method of determining gaseous contaminates, which would overcome the disadvantages of prior art devices, is most desirable.